Slash marks were clearly indicated to illustrate how the phrases would be divided and where Roberts would pause, to ensure the president-elect would be on the same page.

No one is sure why it happened, but "the oath card never reached anyone on Barack Obama's staff," Toobin wrote.

They were concerned enough about the small stumble in the sequencing of words on the inaugural platform that Obama and Roberts went through it again the next day in private in the White House Map Room - just to make sure they were square with the Constitution.

Back at the White House four years later, it all went off without a glitch just before noon on Sunday.

With Roberts waiting in the Blue Room, Obama strode in before a small gathering. He placed his left hand on a Bible belonging to his wife's family and raised his right hand.

Roberts had the card with him and the slash marks identifying where he would pause were clearly visible.

President Barack Obama said Monday in his inaugural speech that the nation must come together to meet the challenges of the day, saying: "We are made for this moment, and we will seize it - so long as we seize it together."